This invention relates to a phased array antenna system and more particularly to a phased array antenna system which can effectively exhibit an antenna pattern with very low sidelobes.
It is known in the art that the performance of steerable phased array antenna systems is largely dependent upon the characteristics of the phase shifters incorporated in such an antenna system. That is, the type of phase shifters used, variations between such devices due to different ambient temperature and operating frequencies, and small variations caused by manufacturing tolerances combine to limit the overall accuracy of the antenna system. This erratic performance of the phase shifters can result in the wide angle sidelobes increasing considerably in amplitude as compared to their theoretical value. With increased sidelobes, the danger exists that the radar system will detect an erroneous target through a sidelobe rather than the intended target via the main beam. Integration of the returned echo pulses for stable targets does not solve the problem with respect to phase as all phase shifters have heretofore been fixed for a sequence of pulses which are integrated in order to maintain precision with respect to the main beam's direction.
Prior work in this area includes U.S. Pat. No. 3,412,405 to Crotty et al which discloses a system for reducing the sidelobe response of a receiving antenna which continuously shifts the phase center of the antenna. Also, U.S. Pat. No. 4,308,539 to Birch shows a phased array antenna wherein the drive to each one of a plurality of phase shifters is changed to compensate for changes in operating conditions. While each of these patents is suitable for their intended purpose, neither invention effectively reduces the sidelobes in a phased array antenna system in order to easily distinguish a main beam response from a sidelobe re- sponse.